Most spray type applicators involve the use of a wide boom, carrying spaced spray nozzles, mounted on the rear of a vehicle, e.g. a two-wheel cart, a tandem wheel cart, or a truck, which also carries a tank for the liquid. A boom consists of a metal frame with a hose or pipe running along the frame with outlets for nozzles at regular intervals. The boom sections or wings extending beyond the opposite sides of the vehicle must fold up for transport on roads, and should have safe latches to prevent their coming loose on a road as they might smash against another vehicle. Booms usually are equipped with chain supports mounted on springs and shock absorbers to prevent excessive bounce and damage on rough ground. They must be extremely durable as they frequently hit trees, poles, and hummocks of earth. Even the best booms frequently are badly damaged in normal use, requiring extensive and expensive repair and time lost during a period when application time is critical.
Large farm corporations and chemical distributors, who apply liquid fertilizers for a fee, constantly exert pressure on manufacturers to build wider and wider booms capable of operating at higher and higher speeds, and to equip these booms with sophisticated anti-bounce and shock absorber systems, and with cab controlled means, usually hydraulic, for folding, leveling and adjusting height. Consequently a wide truck boom today may look like a bridge truss, and weigh almost as much. The electric controls, with signal lights, for the hydraulic cylinder valves remind one of the instrument panel of an airplane. Considerable training is necessary to prepare a driver for operating such a system.
A large truss-type boom typically may have outer hinged wing sections about 22 feet long which weigh about 250 pounds. The entire boom assembly typically may weigh about 850 pounds. The cost of such a boom and controls therefor is more than half the cost of the entire system, less the cost of the truck and the supply tank. In contrast, it is estimated that the total list price of a comparable boomless sprayer mechanism embodying this invention will be from 10 to 15 percent of the cost of a 50 foot boom and controls therefor, with shipping weights in about the same proportion.
Truck carried boom sprayer applicators, as disclosed in U.S. Pat. No. 4,267,971, granted May 19, 1981, almost always use so-called "Floodjet" spray nozzles of different size, i.e. K20 through K180, made by Spraying Systems Co. of Bellwood, Ill. With a boom sprayer, however, equipped with such nozzles, the ground-impact pattern of the spray from each nozzle varies in swath width with the pressure of the liquid supplied to the nozzle. Such pressure is varied to vary output rate. At high pressures, the patterns of adjacent nozzles overlap excessively, while at low pressures there may be no overlap at all.
Thus, for example, with a boom sprayer equipped with K50 nozzles spaced on 5 foot centers, if the pressure is such that the swath width of the pattern of each nozzle is 7.5 feet, every other 2.5 feet wide swath of the overall pattern has double the amount of liquid applied thereto as the swaths inbetween. Further, if a boom sprayer makes a pass through a field at high speed and nozzle pressure, producing an overall wide pattern, and the adjacent pass is at low speed and nozzle pressure producing a narrower overall pattern, the application rate will be very uneven near the adjacent edges of the passes. Additionally, the sprays from adjacent boom-mounted nozzles frequently collide or run together which causes a heavy concentration of the spray falling to the ground when the two sprays collide.
Attempts have been made to overcome some of the foregoing problems attendant boom sprayers by developing boomless sprayer type applicators, and some have even made and marketed. One type, presently on the market, is in the form of a cluster of nozzles arranged radially about a common manifold to throw a fan-shaped spray laterally outwardly on both sides of the vehicle, and also downwardly. The plane of the spray is generally vertical so that the spray will impact the ground in a pattern generally in the shape of a narrow band moving transversely of its length, which length is the swath-width of the pattern or application. This type of nozzle arrangement has not proven to be practical, however, because:
1. The swath width is not constant, as is necessary, varying over 100 percent from low output rates to high output rates which are determined by the pressure of the liquid supplied to the cluster. PA1 2. Part of the spray is directed upwardly away from the ground so that it is easily deflected by wind, causing the ground-impact pattern to be distorted. PA1 3. No means is provided for marking the swath, as with a ground dye spot, in order to provide the operator with means for locating the correct truck path for an even field coverage.